1. Field of the Invention
This invention relates generally to hard disk drives, and more particularly to methods for increasing the density of data stored on a media while maintaining precise positioning capabilities.
2. Description of the Related Art
Hard disk drives are common in most modern computer systems. Generally, a hard disk is used as a storage unit for data that is not currently being used by a CPU, but may be periodically accessed. Recently, there has been a growing demand for increased storage space on hard disks. This demand is due in part to the increased complexity and size of computer programs and the need to archive an increased number of data files, e-mail files, graphics files, etc.
To enable the storage of data onto a hard disk, the manufacture is generally required to format the hard disk. Hard disks are generally formatted to have a plurality of circular tracks that are divided into sectors. By way of example, FIG. 1A shows an exemplary sector 120 that may be repeated around a particular track. In this example, the sector 120 is shown having a header section 121, a data section 122 and an error correction code (ECC) section 124. As is well known in the art, the header section may be used to store an exact sector address, for example, of sector 120. In this manner, the writing or reading mechanism used by a hard disk unit will be able to identify the exact address of a sector. Although the inclusion of the header section 121 for address identification is quite useful and well known, the demand for increased storage density on hard disk media has driven designers and manufactures to modify the formatting of the media tracks.
For example, FIG. 1B shows a more compact sector 120' having a data section 122 and an ECC section 124. Clearly, compact sector 120' will enable the storage of substantially more data in a given media because the header section 121 of sector 120 is no longer used. Although more data can be stored on the media without the inclusion of headers, identifying a correct desired sector will become more difficult than before. Several techniques are typically used to enable the identification of a correct desired sector. One technique utilizes what are known as "seed bytes" to identify the address of each sector. Before the data sector 120' is written to the media, an ECC calculation is performed over the ECC section 124, the data section 122 and a seed section 126. Once the ECC calculation is performed, only the data section 122 and the ECC section 124 are written to the media in the form of sector 120'.
Now that the data is written to the media, a read operation to locate a desired sector having a particular address is performed. The request for a particular desired sector address is generally triggered by a host that asks for the retrieval of a particular sector which will have an associated seed byte (e.g., seed byte 55). The hard disk drive circuitry and mechanical arm (not shown) then attempts to find the approximate location of the desired sector by performing well known indexing, and sector pulsing for each revolution of the media. Other techniques, such as servo split identification may also be used to approximately locate the desired sector, however, the inclusion for servo splits will require additional space on the media, which is counter productive to increasing storage space through headerless sectors.
Once the disk drive circuitry locates a sector that it believes to approximate the location of the desired sector, an ECC computation will be performed over the retrieved ECC section 124, data section 122 and a seed section 126 for the desired sector (i.e., seed byte 55). However, it should be noted that the seed section 126 is not stored on the media, rather, it is provided once the host requests the desired sector. If one of the seed byte locations is found to be in error (i.e., by producing a "seed error") after the ECC calculation, then the retrieved sector and the desired sector will not be the same. In other words, the disk drive will only know that it did not find the requested sector and will therefore be required to continually repeat the search until the retrieved sector and the desired sector match. Although an increased data storage density is achieved by storing data on a media without headers, positioning and retrieval of a desired sector becomes a sluggish and repetitive task that may be impact the long term reliability of a disk drive system.
In view of the foregoing, there is a need for a method and apparatus that enables high density data storage while providing rapid and precise positioning to a desired sector in a given media.